Not applicable.
Not applicable.
The present invention relates to corrosion-inhibited fire retardant compositions. More specifically, the invention is directed to ammonium polyphosphate concentrates and other solutions containing suspended and/or soluble iron compounds having a reduced corrosion tendency.
Aerial application of fire-retardant compositions to combat the spread of wildland fires is common. Fire retardant compositions designed for managing and controlling wildland fires are of two general types, dry-powdered concentrates that are mixed with water prior to use and concentrated liquids, which are diluted with water at the time of transfer to an application vehicle. Fire retardant concentrates that are supplied in the liquid form are preferred by some because they can be simply and easily diluted to end-use strength with little mixing hardware and manpower.
Ammonium polyphosphate liquids have been used as aerially applied fire-retardants. These liquids have certain advantages in comparison to other fire-suppressing compositions since they can be transported and stored prior to use in the liquid form rather than being mixed from dry ingredients. However, concentrated liquid fire retardants and solutions prepared therefrom are extremely corrosive to aluminum and brass and mildly corrosive to other materials of construction used in handling, storage and application equipment. As used herein, all metals include alloys thereof. Accordingly, aluminum includes aluminum 2024T3, 6061 and 7074, steel includes 1010 and 4130 steel and brass includes yellow and naval brass. Since wildland fire retardants are most frequently transported to the fire and applied aerially, it is imperative that corrosive damage to the materials of construction of fixed-wing aircraft and helicopters be minimized.
Accordingly, the United States Department of Agriculture (xe2x80x9cUSDAxe2x80x9d) Forest Service has established, in xe2x80x9cSpecification 5100-304b (July 1999) Superseding Specification 5100-00304a (February 1986),xe2x80x9d entitled xe2x80x9cSpecification for Long Term Retardant, Wildland Fire, Aircraft or Ground Applicationxe2x80x9d (hereinafter, xe2x80x9cForest Service Specificationsxe2x80x9d), hereby incorporated by reference in its entirety, maximum allowable corrosion rates for 2024T3 aluminum, 4130 steel, yellow brass and Az-31-B magnesium. For example, the corrosivity of forest fire retardants, in concentrate, to aluminum, steel, yellow brass and magnesium must not exceed 5.0 milli-inches (xe2x80x9cmilsxe2x80x9d) per year as determined by the xe2x80x9cUniform Corrosionxe2x80x9d test set forth in Section 4.3.5.1 of the aforementioned USDA, Forest Service Specifications. The Forest Service Specifications identify the maximum amount of corrosion acceptable when both the retardant concentrate and its diluted solutions are exposed to each metal indicated above at temperatures of 70xc2x0 Fahrenheit (xe2x80x9cFxe2x80x9d) and 120xc2x0 F. in both totally and partially immersed configurations. The maximum allowable corrosivity of aerially applied fire retardant diluted solutions to aluminum is 2.0 mils per year (xe2x80x9cmpyxe2x80x9d) and the maximum corrosivity to brass and steel is 2.0 mpy when partially immersed and 5.0 when tested in the partially immersed condition. In the partially immersed configurations, one-half of the coupon is within the solution and one-half is exposed to the vapors in the air space over the solution.
In an effort to address the corrosivity problems encountered with the use of fertilizer grade ammonium polyphosphates, sodium ferrocyanide was incorporated into the corrosive compositions. Sodium ferrocyanide has proven to be an effective corrosion inhibitor in fire retardant compositions containing ammonium polyphosphate fertilizer solutions. However, while sodium ferrocyanide is effective as a corrosion inhibitor, several disadvantages of its use make its incorporation in wildland fire retardant compositions unacceptable. Specifically, the environmental and toxicological safety of ferro(i)cyanides is, at best, questionable. When exposed to acidic conditions and/or ultraviolet radiation from natural sunlight, the ferro(i)cyanide radical readily degrades releasing free iron and cyanide and/or hydrogen cyanide, which are toxic to humans, animals and aquatic life. Further, free iron emanating either from decomposition of a portion of the ferro(i)cyanide radical, or introduced from other components or impurities within the composition, will subsequently react with remaining non-decomposed ferro(i)cyanide to form ferricyanide (xe2x80x9cTurnbull""s Bluexe2x80x9d) or ferrocyanide (xe2x80x9cPrussian Bluexe2x80x9d), which emit a persistent blue-black coloration, staining all that they contact. Consequently, neither ferricyanide nor ferrocyanide can be used in fire-retardants that are expected to fade and become non-visible over time, for example, in fugitive retardant compositions. The magnitude of the above concerns is increased since wildland fire retardants are generally applied aerially in a less than completely controlled manner. Due to the presence of variables such as vegetative cover, smoke, or wind drift that impact the trajectory of the free-falling solution, aerially applied wildland fire retardant solutions may land on or near people, animals and in bodies of water or on soil where it could enter the water supply.
Accordingly, there is a need to provide safe and acceptable wildland fire retardants for the suppression or management of wildland fires that are not corrosive to the equipment associated with the transportation, handling and application of the retardant and that are both environmentally and toxicologically friendly, thereby avoiding the above disadvantages.
In overcoming the above disadvantages, it is an object of the invention to produce a wildland fire retardant composition that has a reduced-tendency to corrode various metals, and does not decompose with exposure to sunlight or acidic conditions, resulting in the release of toxic by-products that could be both environmentally and toxicologically hazardous.
It is a further object of the invention to provide a fire retardant composition that is compatible with the concept of a fugitive or fading color system, able to become invisible over time with exposure to natural sunlight.
The above and other objects are met by the present invention, which provides a corrosion-inhibited fire retardant composition including at least one fire retardant composition that includes at least one ammonium polyphosphate, at least one suspending agent and a corrosion inhibiting system that includes at least one corrosion inhibiting compound selected from a group of compounds consisting of azoles, insoluble ferric pyrophosphate, soluble ferric pyrophosphate (mixture or blend of sodium citrate and insoluble ferric pyrophosphate), ferrous oxalate, ferric citrate, ferrous sulfate, ferric ammonium citrate, insoluble ferric orthophosphate, soluble ferric orthophosphate, ferric ammonium oxalate, ferric ammonium sulfate, ferric bromide, ferric sodium oxalate, ferric stearate, ferric sulfate, ferrous acetate, ferrous ammonium sulfate, ferrous bromide, ferrous gluconate, ferrous iodide, ferric acetate, ferric fluoroborate, ferric hydroxide, ferric oleate, ferrous fumarate, ferrous oxide, ferric lactate, ferric resinate, and any combination thereof; wherein the corrosion inhibiting system is present in a minor effective amount to substantially reduce the corrosiveness of the fire retardant composition.
In a second aspect, the present invention provides a method of preparing the above-described corrosion-inhibited fire retardant compositions of the invention that includes the steps of forming an intermediate concentrate composition suitable for transportation and storage that includes the above-described corrosion-inhibited fire retardant composition of the invention; wherein the corrosion inhibiting system is present in a minor amount effective to substantially reduce the corrosivity of the fire retardant composition of the invention and diluting the intermediate concentrate with water to form the corrosion-inhibited fire retardant compositions of the invention.
In yet a third aspect, the present invention provides a method of suppressing wildland fires that includes aerially applying to wildland vegetation, ahead of wildland fire, a fire suppressing composition that is comprised of water and the above-described corrosion-inhibited fire-retardant compositions of the invention.
In a fourth aspect, the present invention provides a method of inhibiting corrosion that includes providing a corrodible material and contacting it with an effective amount of the above-described corrosion inhibiting system of the invention.
In a fifth aspect, the present invention provides a corrosion-inhibited agricultural plant nutrient that includes at least one agricultural plant nutrient and the above-described corrosion inhibiting system of the invention. Generally, the corrosion inhibiting system is present in a minor amount effective to substantially reduce the corrosiveness of the agricultural plant nutrient.